U.S. patent application number 12/279810 was filed with the patent office on 2009-01-15 for device for controlling the movement of a valve, in particular of an intake valve, of an internal combustion engine.
This patent application is currently assigned to Fiat Auto S.p.A.. Invention is credited to Mario Palazzetti, Stefano Re Fiorentin.
Application Number | 20090013944 12/279810 |
Document ID | / |
Family ID | 37487579 |
Filed Date | 2009-01-15 |
United States Patent
Application |
20090013944 |
Kind Code |
A1 |
Re Fiorentin; Stefano ; et
al. |
January 15, 2009 |
DEVICE FOR CONTROLLING THE MOVEMENT OF A VALVE, IN PARTICULAR OF AN
INTAKE VALVE, OF AN INTERNAL COMBUSTION ENGINE
Abstract
The device is adapted to control the movement of a valve (1) of
an internal combustion engine comprising a stem (1a) which may move
in translation through an opening (2a) of a hollow guide body (2)
and which ends in a mushroom head (1b) cooperating in operation
with a valve seat (12) provided in a wall (13) of the engine head.
The valve (1) may move in translation with respect to the hollow
guide body (2) between a retracted position and a forward position
in which the mushroom head (1b) respectively closes and opens the
associated valve seat (12). The control device comprises an
electromagnet (3) adapted, when energised, to retain the valve (1)
in the retracted closed position, a first spring (7) associated
with the valve (1) and tending to urge it towards the open
position, and a second spring (8) also associated with the valve
(1) and tending to oppose its transition into the open position.
The arrangement is such that when the electromagnet (3) is
de-energised, the valve (1) moves in acceleration towards the open
position under the action of the first spring (7) until the action
of the latter stops, and then the valve (1) moves in deceleration
into the open position under the action of the second spring
(8).
Inventors: |
Re Fiorentin; Stefano;
(Grugliasco (Torino), IT) ; Palazzetti; Mario;
(Avigliana (Torino), IT) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
Fiat Auto S.p.A.
Torino
IT
|
Family ID: |
37487579 |
Appl. No.: |
12/279810 |
Filed: |
February 22, 2007 |
PCT Filed: |
February 22, 2007 |
PCT NO: |
PCT/IB2007/050566 |
371 Date: |
August 18, 2008 |
Current U.S.
Class: |
123/90.11 |
Current CPC
Class: |
F01L 3/22 20130101; F01L
1/46 20130101; F01L 9/20 20210101 |
Class at
Publication: |
123/90.11 |
International
Class: |
F01L 9/04 20060101
F01L009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2006 |
IT |
TO2006A000131 |
Claims
1. A device for controlling the movement of a valve, in particular
of an intake valve of an internal combustion engine, comprising a
stem adapted to move in translation through an opening of a hollow
guide body and which ends in a mushroom head cooperating in
operation with a valve seat provided in a wall of the engine head,
wherein the valve is adapted to move in translation with respect to
the hollow guide body between a retracted position and a forward
position in which the mushroom head respectively closes and opens
the associated valve seat, the control device being characterised
in that it comprises an electromagnet adapted, when energised, to
retain the valve in the retracted closed position, first resilient
means associated with the valve and tending to urge it towards the
open position, and second resilient means also associated with the
valve and tending to oppose its transition into the open position,
the arrangement being such that when the electromagnet is
de-energised, the valve moves in acceleration towards the open
position under the action of the first resilient means until the
action of the latter stops, and then the valve moves in
deceleration into the open position under the action of the second
resilient means.
2. A device according to claim 1, wherein, when the electromagnet
is de-energised, the mushroom head, starting from the retracted
closed position, may, under the action of the first resilient
means, move in translation, substantially in a tight manner or with
a limited play, into a recess of the wall of the head facing the
combustion chamber with which the valve is associated, until the
action exerted on the valve by the first resilient means ceases,
the arrangement being such that when the engine is off the valve is
retained by the first and second resilient means in a position of
equilibrium in which the mushroom head does not protrude from this
recess into the combustion chamber and is preferably disposed
substantially flush with this wall.
3. A device according to claim 1, wherein the first and second
resilient means comprise a respective first and second helical
spring disposed about the stem of the valve in the hollow guide
body and acting on opposite sides on a transversely projecting
formation of the stem of the valve.
4. A device according to claim 1, wherein a ferromagnetic keeper
cooperating with the electromagnet is connected to the end of the
stem of the valve opposite the mushroom head.
5. A device according to claim 4, wherein the electromagnet
comprises a pot-shaped magnetic circuit having a central projection
or expansion facing the keeper and about which an excitation
winding is disposed.
6. A device according to claim 4, wherein the keeper may slide in a
substantially tight manner into a passage defined in the magnetic
circuit of the electromagnet.
7. A device according to claim 1, wherein the guide body forms a
housing in which the electromagnet, the valve and the first and
second resilient means are pre-assembled in order to form a single
overall unit or pre-assembled cartridge.
Description
[0001] The present invention relates to a device for controlling
the movement of a valve, in particular of an intake valve, of an
internal combustion engine.
[0002] The invention relates more particularly to a device for
controlling the movement of a valve comprising a stem which is
adapted to move in translation through an opening of a hollow guide
body and which ends in a mushroom head cooperating in operation
with a valve seat provided in a wall of the engine head, wherein
the valve is adapted to move in translation with respect to the
hollow guide body between a retracted position and a forward
position in which the mushroom head respectively closes and opens
the associated valve seat.
[0003] The object of the present invention is to provide a control
device which makes it possible to achieve a substantially constant
duration of the period of actual opening of the valve irrespective
of the speed of revolution (rpm) of the engine.
[0004] In practice, a constant duration of the period of opening of
the intake valve makes it possible to achieve different load values
by acting on the phasing of this period. When this period straddles
the bottom dead centre, where the underpressure in the combustion
chamber reaches a maximum, full load conditions are obtained.
However, the more the period of opening of the valve, appropriately
delayed, is partially in the compression phase, the more partial
load conditions are achieved. Opening of the intake valve at the
bottom dead centre brings about the so-called "hammer" phenomenon
which makes it possible to achieve high volumetric efficiency
values (supercharging effect), provided that the duration of
opening of the valve is such that its closure is ensured before
reflux conditions occur.
[0005] This and other objects are achieved by the invention which
relates to a control device of the type described above,
characterised in that it comprises: [0006] a stationary
electromagnet adapted, when energised, to retain the valve in the
retracted closed position, [0007] first resilient means associated
with the valve and tending to urge it towards the open position,
and [0008] second resilient means also associated with the valve
and tending to oppose its transition to the open position, [0009]
the arrangement being such that when the electromagnet is
de-energised, the valve moves in acceleration towards the open
position under the action of the first resilient means until the
action of the latter stops, and then the valve moves in
deceleration into the open position under the action of the second
resilient means.
[0010] According to a further characteristic feature, when, in a
control device of the invention, the electromagnet is de-energised,
the mushroom head, starting from the retracted closed position,
may, under the action of the first resilient means, move in
translation, substantially in a tight manner or with a limited
play, into a recess of the wall of the head facing the combustion
chamber until the action exerted on the valve by the first
resilient means ceases; the arrangement is then such that when the
engine is off the valve is retained by the first and second
resilient means in a position of equilibrium in which the mushroom
head does not protrude out of this recess into the combustion
chamber and is preferably disposed substantially flush with this
wall.
[0011] As will be explained in further detail below, the control
device of the invention may, together with the valve itself, be
formed as a self-contained unit which may be inserted in a
corresponding seat provided in the engine head.
[0012] Further characteristic features and advantages of the
invention are set out in the following detailed description, given
purely by way of non-limiting example and made with reference to
the accompanying drawings, in which:
[0013] FIG. 1 is a diagrammatic view in section of an intake valve
of an internal combustion engine associated with a control device
of the present invention, the valve being in the retracted closed
position;
[0014] FIG. 2 in a view in section similar to that of FIG. 1,
showing the valve and the associated control device of the
invention in a condition of equilibrium;
[0015] FIG. 3 is a view in section similar to those of the
preceding Figures, showing the valve in the open position;
[0016] FIG. 4 is a Cartesian diagram showing, as a function of the
time shown on the abscissa, the curve of the lift of a valve
associated with a device for controlling movement of the present
invention.
[0017] In FIGS. 1 to 3 of the accompanying drawings, a valve of an
internal combustion engine, in particular an intake valve, is shown
overall by 1.
[0018] In a known manner, the valve 1 comprises a stem 1a which
ends at one end with a mushroom head 1b.
[0019] The stem 1a of the valve 1 is mounted to move in translation
through an opening 2a in an end wall 2b of a hollow support and
guide housing shown overall by 2.
[0020] On the side oppose the wall 2b, an electromagnet shown
overall by 3 is housed in the housing 2. In the embodiment shown,
this electromagnet comprises a pot-shaped magnetic circuit 4 having
a central projection or polar expansion 4a surrounded by a
substantially cylindrical jacket 4b. The excitation winding 5 of
this electromagnet is disposed about the projection 4a within the
jacket 4b. The end of the stem 1a opposite the mushroom head 1b
bears a keeper 6 of ferromagnetic material facing the central
portion 4a of the magnetic circuit 4 of the electromagnet 3.
[0021] Two helical springs, shown respectively by 7 and 8, are
disposed about the stem 1a of the valve 1 in the support and guide
body or housing 2.
[0022] The upper spring 7 extends between the electromagnet 3 and a
plate 9 rigid with an intermediate portion of the stem 1a of the
valve.
[0023] The lower spring 8 extends between the plate 9 and the lower
end wall 2b of the support and guide housing 2.
[0024] The assembly formed by the valve 1, the support and guide
housing 2 and the other components described above substantially
forms a kind of independent "cartridge", which can therefore be
pre-assembled and readily mounted in a corresponding seat 10
provided in the head of the combustion engine, this seat
intersecting the end portion of the intake duct 11 with which the
valve 1 is associated.
[0025] The mushroom head 1b of the valve 1 cooperates with a valve
seat 12 provided in a wall 13 of the head of the internal
combustion engine.
[0026] In operation, in the manner described below, the valve 1 may
move in translation between a retracted position (FIG. 1) in which
the mushroom head (1b) closes the valve seat 12 and a forward
position (FIG. 3) in which the mushroom head (1b) protrudes into
the combustion chamber 14, providing the maximum opening.
[0027] A recess 15 adjacent to the valve seat 12 is provided on the
side of the wall 13 facing the chamber 14. The mushroom head 1b of
the valve may slide tightly or with a limited play in this
recess.
[0028] When the winding 5 is energised, the electromagnet 3
attracts the ferromagnetic keeper 6 and retains the valve 1 in the
retracted closed position of FIG. 1. In this condition, the upper
spring 7 (whose elastic constant will be shown below as K.sub.1) is
compressed between the plate 9 and the electromagnet 3. The lower
spring 8 (whose elastic constant will be shown below as K.sub.2)
is, however, unloaded.
[0029] When the winding 5 of the electromagnet 3 is de-energised,
the valve 1 is no longer electromagnetically retained in the
retracted closed position, and under the action exerted on it by
the upper spring 7, it moves downwards with an accelerating
movement until it reaches a position of equilibrium shown in FIG.
2; in this condition, both springs 7 and 8 are substantially
unloaded and in equilibrium with one another and the valve 1 is
held in a position in which the mushroom head 1b again extends
within the recess 15 without projecting into the combustion chamber
14, preferably with its lower end surface substantially flush with
the lower surface or face of the wall 13. In FIG. 1, the stroke of
the valve 1 between the retracted closed position and the position
of equilibrium shown in FIG. 2 has an extension L.sub.2. This
extension L.sub.2 is substantially equal to the extent of
pre-compression of the spring 7 with the valve 1 closed.
[0030] As a result of the presence of the recess 15 of extension
L.sub.2, the pressure differential between the intake duct 11 and
the combustion chamber 14 at the moment at which it is desired to
open the valve helps to impart a quantity of movement to this valve
1. Similarly, during the phase of further closing of the valve,
when the associated piston of the combustion engine is rising
again, the pressure differential (this time of opposite sign) tends
to urge the mushroom head 1b of the valve 1 into the recess 15,
promoting the closure of the valve.
[0031] In practice, the mechanical work performed as a result of
the above pressure differentials is useful in compensating the
energy dissipated as a result of friction forces.
[0032] An equation of the movement of the valve 1 during the
opening phase will now be described.
[0033] When the electromagnet 3 is de-energised, the valve 1 is
subject to the concurrent thrusts exerted by the upper spring 7 and
by the air pressure in the intake duct 11.
[0034] Using an x-coordinate axis oriented downwards (FIG. 1, where
x=0 corresponding to the closed position of the valve 1), the force
F.sub.air which the pressure differential .DELTA.p between the
intake duct 11 and the combustion chamber 14 exerts on the mushroom
1b of the valve may be expressed as a function of the stroke x by
the relationship:
F.sub.air(x)=.DELTA.p(x).S
where S is the exposed surface of the valve.
[0035] For simplicity, and as a rough approximation, the following
assumptions may be made as regards the pressure differential
.DELTA.p(x): [0036] during the phase of opening of the valve, as
long as the valve is still closed as it is moving in the recess 15,
it can be assumed that the pressure differential (positive, i.e.
with an underpressure in the chamber 14) is:
[0036] .DELTA. p ( x ) = p 0 , where x .ltoreq. L 2 and x t > 0
##EQU00001## [0037] during the phase of actual opening
(x>L.sub.2), it is assumed that .DELTA.p(x) is zero:
[0037] .DELTA.p(x)=0, where x>L.sub.2; [0038] during the phase
of closure of the valve, when the latter returns to the recess 15,
it is assumed that the pressure differential is inverted:
[0038] .DELTA. p ( x ) = - p 0 , where x .ltoreq. L 2 and x t <
0 ; ##EQU00002##
[0039] The forces of the springs 7 and 8 then act on the valve
1:
[0040] Upper spring: this spring exerts a force
F.sub.1(x)=K.sub.1(L.sub.2-x) and F.sub.2(x)=0, where
x.ltoreq.L.sub.2.
[0041] Lower spring: this spring exerts a force
F.sub.2(x)=0 and F.sub.2(x)=K.sub.2(L.sub.2-x), where
x>L.sub.2.
[0042] Lastly, the friction forces between the stem 1a of the valve
and the guide opening 2a, and between the plate and the surrounding
wall of the support and guide housing 2, also play a part. In
relation to these friction forces, it can be assumed that they can
be described by a constant term of sign opposite that of the
velocity of the valve, as a result of the pressure of the sealing
members (present, but not shown in the drawings) and by a term
proportional to the modulus of the velocity of opening of the valve
1:
F f = - ( a x / t + b ) x t ##EQU00003##
in which a and b are damping coefficients.
[0043] This provides the following equation of movement:
m 2 x t 2 = .DELTA. p ( x ) S + F 1 ( x ) + F 2 ( x ) - ( a x / t +
b ) x t + m g ##EQU00004##
[0044] On the basis of the equation of movement given above, it is
possible to calculate the values of some parameters of the device
for controlling the movement of the valve.
[0045] Let us assume, for instance, that it is wished to achieve an
overall time of actual opening of the valve (i.e. the time during
which the mushroom 1b is disposed externally to the recess 15) of
between 5 and 6 ms.
[0046] The following values are assumed for the area and the mass
of the valve 1,
[0047] S=7 cm.sup.2 and m=30 g.
[0048] Reasonable values for the damping coefficients are, for
instance, as follows:
[0049] .alpha.=5 N and b=1.5 Ns/m
[0050] On the basis of the above numerical data, a time of actual
opening of the order of 5/6 ms is obtained with the following
values of the parameters L.sub.2, K.sub.1 and K.sub.2: [0051]
L.sub.2=4.0 mm [0052] K.sub.1=105000 N/m [0053] K.sub.2=11800
N/m
[0054] In order to prevent knock in the closing phase of the valve,
which occurs when the work due to the pressure differential exceeds
the energy lost by friction, it may be advantageous to provide a
pneumatic brake in the last part of the closure stroke of the valve
1, between the magnetic keeper 6 and the electromagnet 3. To this
end, provision may be made for the movement of the keeper 6 to take
place substantially in a tight manner relative to the polar
expansions of the magnetic circuit 4.
[0055] On the basis of the numerical data given above, the lift
profile of the valve 1 as a function of the value assumed for
p.sub.0 (pressure differential in the phase of movement of the
mushroom 1b within the recess 15) is shown in FIG. 4.
[0056] As can be seen in this Figure, the maximum lift of the valve
is equal to 12 mm with an actual opening time of 5 ms.
[0057] The values of the retaining force which the electromagnet 3
has to exert for the three values of p.sub.0 to which the graphs of
FIG. 4 refer are as follows: [0058] p.sub.0=0.9 bar: F=483 N [0059]
p.sub.0=0.7 bar: F=469 N [0060] p.sub.0=0.5 bar: F=455 N
[0061] If the magnetic force exerted on the keeper 6 is described
by the expression F=sB.sup.2/(2.mu..sub.0) and if it is assumed
that s=3 cm.sup.2 (area of the section of the portion 4a of the
magnetic circuit 4 of the electromagnet), the following value is
obtained for the magnetic induction B:
B = 2 .mu. 0 F s = 2 4 .pi. 10 - 7 [ N / A 2 ] 483 [ N ] 3.0 10 - 4
[ m 2 ] = 2.0 [ N / A m ] = 2.0 [ T ] ##EQU00005##
[0062] In operation, the control device of the valve is initialised
when the first compression occurs in the associated cylinder of the
engine: the pressure in the combustion chamber 14 causes the full
closure of the valve 1 until the keeper 6 is hooked by the
energised electromagnet 3.
[0063] Associating respective devices for controlling movement of
the present invention with the intake valves of an internal
combustion engine makes it possible to achieve the opening of these
valves in a fixed time, irrespective of the number of revolutions
per unit of time of the engine.
[0064] The exhaust valves may be traditionally controlled, for
instance by a camshaft, or by associated devices for controlling
movement of the type described above, obviously driven with a
different phasing.
[0065] Without prejudice to the principle of the invention, its
embodiments and details may obviously be widely varied with respect
to what has been described and illustrated purely by way of
non-limiting example, without thereby departing from the scope of
the invention as set out in the accompanying claims.
* * * * *